Located within Ueno Station, the Ecute shopping mall is home to a variety of stores and restaurants, and one fantastic spot for vegetarians and vegans is T's Tantan on the third floor of the venue. The Ueno store is one of several T's Tantan locations across Tokyo (others can be found at Tokyo Station, Ikebukuro Station, and Narita Airport), and the chain has become famous for serving up vegan-friendly ramen without the use of typical ingredients like meat, seafood, or eggs.
This branch of T's Tantan has more than just ramen on offer though — there are numerous other hearty vegan meals for guests to try. The vegan hamburger steak served with a mushroom sauce (¥ 2,000 including tax), the grilled soy meat plate served with colorful veggies (¥ 1,380), and the cold yuzu shoyu noodles with soy pork (¥ 1,450) are just some of the tasty options available. For celiacs or those who choose to eat gluten-free, the usual noodles can be substituted for gluten-free ones - just ask when you're placing your order. If you're visiting with kids in tow, they also have a kids plate which comes with a mini salad, a main dish (your choice of either "meat" sauce served over rice or a vegetable curry), and either orange or apple juice.
For folks who live in the local area, the store also offers a number of their products available for takeout or delivery. The to-go menu options can be found in PDF format here.